[Bug libstdc++/81522] New: c++17/old-abi/cygwin empty stringstream invalid memory access

["irfanadilovic at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81522

            Bug ID: 81522
           Summary: c++17/old-abi/cygwin empty stringstream invalid memory
                    access
           Product: gcc
           Version: 7.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: irfanadilovic at gmail dot com
  Target Milestone: ---
             Build: x86_64-pc-cygwin

This trivial program:

#include <sstream>
int main() {
    std::stringstream os; // same with ("") or (std::string())
    os.str();
    return 0;
}

causes an invalid memory access with gcc 7.1.0 (compiled from source), but only
on Cygwin in c++17 mode with old ABI, and only if the stringstream is
constructed empty. Changing any of those parameters no longer causes the issue.

Thread 1 "string" received signal SIGABRT, Aborted.
0x00000001004018a0 in __gnu_cxx::new_allocator<char>::deallocate (this=0x6,
__p=0x3e8000003fc <error: Cannot access memory at address 0x3e8000003fc>)
    at /usr/local/gcc-7.1.0/include/c++/7.1.0/ext/new_allocator.h:125
125             ::operator delete(__p);
(gdb) bt
#0  0x00000001004018a0 in __gnu_cxx::new_allocator<char>::deallocate (this=0x6,
__p=0x3e8000003fc <error: Cannot access memory at address 0x3e8000003fc>)
    at /usr/local/gcc-7.1.0/include/c++/7.1.0/ext/new_allocator.h:125
#1  0x00000001800b25d2 in CreateEventW () from /usr/bin/cygwin1.dll
#2  0x0000000000000130 in ?? ()

$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/local/gcc-7.1.0/libexec/gcc/x86_64-pc-cygwin/7.1.0/lto-wrapper.exe
Target: x86_64-pc-cygwin
Configured with: ../configure --prefix=/usr/local/gcc-7.1.0
--enable-threads=posix --enable-checking=release --enable-languages=c,c++
--build=x86_64-pc-cygwin --disable-multilib
--with-default-libstdcxx-abi=gcc4-compatible
Thread model: posix
gcc version 7.1.0 (GCC)

Sample program compiled with:

$ g++  -std=c++17 -D_GLIBCXX_USE_CXX11_ABI=0 -ggdb -O0   string.cc   -o string